1. Field of the Invention
The present invention relates to techniques for particle localization by geometrical structures. More specifically, the invention relates to methods and devices for particle localization in geometrically ordered nanostructures and the fabrication of large arrays of artificial atoms and molecules having electronic properties suitable to signal amplification, electrical conductivity, anti-ferromagnetism, and the like.
2. Relevant Technology
Nanotechnology is rapidly evolving field. The race is on to develop self-organizing structures that can be used as active circuit elements. For example, U.S. Pat. No. 6,459,095 B1 discloses a process that traps electrically switchable molecules between crossed wires only a few atoms wide, allowing for the creation of a manufacturable molecular electronic technology. There is also currently a great deal of interest in quantum dots, which are three-dimensional heterostructures measuring about 1 nm (10−9 m) to about 100 nm in each direction, in which electrons, holes and/or excitons may be confined.
Superconductivity, a low temperature phenomenon (T<25 K) that is found in some “bad” metals (Pb, Sn, Hg, Nb, etc.) and their alloys, was discovered a century ago. A fundamental theory was lacking until 1957 when Bardeen (also co-inventor of the transistor), and his students Cooper and Schrieffer developed the Bardeen-Cooper-Schrieffer (BCS) electron-pairing theory that is at the heart of our present-day understanding. In 1986, Berdnoz and Müller found the first “high-temperature superconductor” (HTS), capable of superconductivity at temperatures some 50% higher than the previous best and believed by many researchers to be ultimately capable of exceeding room temperature (20° C.) in future developments. The pairing is the same but the mechanism that causes pairing appears to be novel. Unlike “low” temperature superconductors, the HTS have been found to-date only in the layered CuO2 planes that can occur in crystals of the perovskite type. When each CuO2 unit contains precisely 5 active electrons, the collective behavior is that of a single spin ½. Each CuO2 plane resembles a spin ½ Heisenberg antiferromagnet, weakly coupled from plane to plane. Even such weak coupling allows for a Néel temperature of up to 1000 K, indicating that the in-plane coupling parameter J is substantial. When electrons are taken away, say a fraction f is removed (f is typically in the range of 5%–25%,) a fraction f of the CuO2 units will acquire spin 0 and a charge +e relative to the other units. This missing electron is called a hole. The presence of holes allows metallic conductivity and superconductivity in CuO2.
Experimentally the BCS energy gap is not isotropic across the Fermi surface in HTS as it is in the low-temperature superconductors, but has nodes corresponding to so-called “d-waves.” The study of many-body systems (e.g., Hubbard model, t-J models) has indicated that holes promote electronic conductivity and superconductivity, that HTS is mediated by the same antiferromagnetic forces measured by J as the antiferromagnet, and that the gap should have d-wave symmetry. However, there is complete disagreement and confusion in the physics community regarding the precise mechanism and the exact model parameters that apply.
Computer simulations of the Hubbard and t-J models have failed to be definitive, owing to the difficulty of solving the many-fermion problem on a sufficiently large lattice—even approximately.
Memory elements are traditionally dichotomic—such as spin “up” or “down.” In giant magnetoresistance (GMR,) a current is modulated by whether two magnetic fields applied to two nearby conducting elements are parallel or antiparallel. But this set-up is difficult to miniaturize, as the power expended in electrical currents can quickly exceed the ability of the material to dissipate and causes meltdown when circuit elements are densely packed.
Microdots have been made out of specially designed semiconductors embedded in a host material. They trap from 1 to 100 electrons, or valence band holes, or combinations of both called “excitons.”
Field effect transistors (FET) are commonly used for weak-signal amplification, d-c switching or signal generation. In a MOSFET (metal-oxide semiconductor FET), the conductivity of a channel is affected by transverse voltage applied at a gate. This metallic gate, acting across a metal-oxide insulating layer, capacitatively charges the channel, thus affecting its conductivity. The gate in the MOSFET has a high input impedance, therefore low input power. The modulation of the channel width by the gate voltage can be large, therefore there is a large output current and power gain inherent in such devices. If the oxide layer is very thin the electrical fields are high and the density of carriers could be changed capacitatively, further optimizing the amplification. But thin dielectrics are fragile, breaking down at or less than 106 v/cm. This limits the ability to modulate charge density by capacitative structures in conventional MOSFETs.